LETTER XLVIII. Phenomena of the Earth. MY DEAR CHILDREN, Whirled 1000 miles an hour,-and not perceive it! you will say; yes, but you do perceive it; you perceive it in the rising of the sun, in his gradual ascent during the day, in his declining and his setting! You see it also in the rising and setting of the stars, and these are all you can feel in regard to it, for all things are carried round together. Perhaps the fly to which I alluded on the roasting meat, knows nothing of his motion, except by the coming and going of distant objects, which in truth stand still; and he may, just as men in former ages did, imagine that the room and the fire are going round, and not the meat and the spit on which he has alighted. We therefore do see our motion on the earth by the apparent motion of the whole universe. The motion of the earth, is, however, like that of a coach wheel-while it turns round it proceeds onward, and in fact it turns round because it moves onward, just as a bowl turns while moving on the grass, and from the same cause it moves one way, while by re-action it turns the other. If, however, you were startled at the notion of 1000 miles an hour, you will be more startled at this progressive motion, which is 68,000 miles an hour, or 68 times faster. But how, you enquire, is this known?because the earth is deter...ined to be 96,000 millions of miles from the sun, and as it goes quite round the sun in a year, so this vast circuit requires a velocity of 68,000 miles an hour. But how, you enquire, is it perceived? By the daily changing of the positions of the stars. If you watch in September the stars which come opposite your window at ten in the evening, you will in Oc tober find other stars at the same hour, and those changes, regular and constant, measure and deter-mine the motion of the earth in its annual orbit round the sun. During this course in the orbit it is that the sun moves day by day through the space called the tropics, causing alternate winter and summer in both hemispheres of the earth. To understand this last change you must place a candle on the table and carry your apple or globe round it, so that on one side it may touch the table, and on the opposite side may rise as much above the level of the candle, and you will then perceive how the perpendicular position of the candle rises and falls with reference to the equator. Such, in truth, is the manner in which the earth revolves round the sun, and hence the changes of seasons and the varied length of days and nights. To acquire a perfect conception of the revolution of the earth, however, you must yourself perform the experiment, and not be content with seeing it performed by another. You will thereby feel and see the effect, and trace the progress of these wonderful changes. These two motions confer, of course, a prodigious force on every body on the earth, but they are so balanced and act so against each other, that instead of hurling or swinging bodies off the earth, they precipitate or direct them towards the centre of the motions, and hence all bodies fall, or endeavour to fall, towards the centre with a force which is called their weight. What a beautiful contrivance of omniscient power by which these motions, which, taken separately, would disperse the whole, are so combined as to be the means of condensing the whole and keeping all the parts together! Such, indeed, are the chief causes and uses of the motions of the planets, but the changes of day and night, and of the seasons, are important and valuable consequences. the whole working together for good, and affording direct proof of divine wisdom and supreme agency. We thus find that we live upon a globe in twofold motion, which motions keep its parts together and direct them to the centre of motion with the force of weight, while they vary the seasons, giving us seed time and harvest time alternately in both hemispheres, and also successions of light for labour, and darkness for rest! LETTER XLIX. The Solar System. MY ESTEEMED Children, You will startle at the mention of such distances as 96 millions of miles, and at motions of 68,000 miles an hour, which is 60 times swifter than a cannon ball; but in such considerations we are not speaking of a house, a garden, or a parish, but of the universe the infinitely-extended or boundless universe. Infinite extension is a wonder of such a nature that if you point in any direction there can be no end or boundary in that direction. For if it be imagined that there is some boundary at any distance, as a million of millions of miles, or a million times more, the question then arises what is there then beyond that point. There must be something -some extension or other, and hence we arrive at the necessary idea that the universe is and must be infinite, or without any assignable bounds. In such an infinite universe, therefore, all imaginable distances, however great, are but comparative points, and millions of miles become ordinary distances, when connected with the great arrangements of the universe. In like manner, I can imagine that you ask me what supports the sun in its place, and what supports the earth in its orbit. This idea of support, or its necessity, arises, however, from your local experience on the earth, where, owing to the earth's motions, every unsupported thing falls towards the centre of the earth; but the sun and the earth are not subordinate to other bodies, like a stone to the earth, and of course have no disposition to fall one way more than another way. Besides, in universal nature there is neither up nor down, the distances being infinite on every side; and every body, like the sun or earth, being indifferent to motion every way, it maintains its station without any necessity for support. Remember, likewise, that on the earth's surface no one part is upward or downward more than another. If we live near the north pole the earth is beneath our feet and the heavens over head, and so at every other part; and all downward, or weight, or falling, is every where directed to the common centre of the earth, as the centre of its motions, or general forces. But the most curious fact is this, that we find that there are other globes revolving round the sun, similar to our globe, but most of them much larger. And it would be an unthinking limitation of Almighty Power, to suppose that in this infinite universe his wisdom was limited to one comparatively small globe. These planets, as they are called, revolve at different distances, two nearer, four more distant than the earth, three of which are equal in size to many hundred earths. The names and distances are Mercury () 37 millions of miles from the sun; Venus (?) 68 millions; the earth () 96 millions; Mars () 144 millions; Jupiter (4) 426 millions; Saturn (h) 730 millions; and Herschel (H) 1800 millions of miles. Doubtless, also, there are others not yet dis covered, and four very small ones, or fragments, have been discovered between (9) and (4) within these very few years, called Ceres, Pallas, Juno, and Vesta. Another curious circumstance also is this, that several of the planets are attended in their orbits by satellites or moons which move round them just as they move about the sun. Thus the earth has one, our noble moon; Jupiter has four, Saturn seven, and Herschel six. Saturn besides is situated in the middle of a ring distant from the planet. All these wonders may be seen by the aid of telescopes of sufficient magnitude. The smallest will, however, show Jupiter's moons, and the interesting face of our own moon. Our sun too has spots which may be discerned with small telescopes if the eye glass is smoked on the inside. Of these wonders there is no end; but for details of the whole I must refer you to the delightful volume on the Wonders of the Heavens. But what will your astonishment be when I tell you that it is rendered probable by facts, that the sun itself, and all its appendages of planets, moons, and their inhabitants, progress round some larger system of which we have as yet no knowledge. This, however, seems to be certain, and that the countless myriads of fixed stars are themselves so many suns to systems of planets like those which surround our sun! What a wonderful-most wonderful scheme of existence and how proper and necessary to be known! LETTER L. The Stars and the Universe. MY ESTEEMED Children, This plurality of worlds established as a fact by astronomy, is one of the most striking traits of hu |